The ecology, behavior, and conservation of migratory birds

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U.S. Geological Survey research contributes to conservation measures and improved management of migratory bird populations and their habitats across the United States. Migratory birds provide ecosystem benefits that include pest control, pollination of plants and serve as food sources for other wildlife. They are also a source of recreation for millions of bird watchers and enthusiasts who provide food and design backyard habitats to attract a variety of species throughout the year. NOROCK researchers are able to explore the behavior and ecology of migratory birds through the unique deployment of tools traditionally used for things such as seafloor mapping, weather forecasting and even military reconnaissance missions. This information can become vital for resource managers to plan conservation measures for migratory bird species into the future.

Thrush feeding babies.

Thrush feeding babies.Public domain

The migrations of most birds comprise time spent in flight interspersed with time spent on the ground. Most migratory flight occurs at night; most resting and refueling between flights – called stopover – occurs during the day. NOROCK scientists and partners are studying the behavior and ecology of birds during flight and stopover using a variety of remote sensing techniques. For example, recent research concerns how migrating birds respond when they encounter barriers to movement such as mountains or oceans. We are finding that prior to crossing the Gulf of Mexico, a 24 hour non-stop flight, many birds will first move inland to fatten up on insects (fat is fuel) before setting out over the water. Not only might are these birds participating in the control of insect populations, they are also showing us what habitats are important to them. In this case, habitats inland from the coast may be vital for their conservation as refueling locations. Weather is likely the primary hazard faced by birds that set out over open water. Usually, the circumstances that lead to bird mortality over open water are difficult to observe. However, a recent study was able to reconstruct the series of events that led to the deaths of nearly 3,000 birds over Lake Michigan.


Solving the mystery of nearly 3,000 birds deaths over Lake Michigan.

Understanding the circumstances that led to the deaths of nearly 3,000 birds along the shores of Lake Michigan is actually a cold case. The deaths occurred 18 years ago, in May 1996. The National Oceanic and Atmospheric Administration (NOAA) maintains numerous weather archives, some going back more than a century. Drawing on archived data from weather stations, open water weather buoys, and weather radar data, we were able to reconstruct the likely sequence of events that led to this mortality.

Weather radar shows migrating birds encountering severe weather over the southern end of Lake Michigan.

Weather radar shows migrating birds encountering severe weather over the southern end of Lake Michigan. On the left, a strong band of precipitation (red) which likely included hail moved over Lake Michigan as birds (much of the blue) were migrating in the same area. The right shows a vertical cross-section of the radar data where the birds occupy the very lowest portions of the atmosphere. The precipitation forms a towering structure 12 km (>39,000 feet) high. This encounter, together with another several days later, is thought to be responsible for the death of nearly 3,000 migrating birds (Diehl et al. 2014).Public domain

Diehl, R. H., J. E. Bates, D. E. Willard, and T. P. Gnoske. 2014. Bird mortality during nocturnal migration over Lake Michigan: a case study. Wilson Journal of Ornithology. 126:19-29.